1. Field of the Invention
The present invention relates to a transparent conductive hard coat film suitably used for a transparent touch panel, etc., and a transparent hard coat film suitable as a substrate for the transparent conductive hard coat film.
2. Related Art
In recent years, liquid crystal display devices have drawn attention as image display devices, and expected applications include portable electronic notebooks, information terminals, etc. As input devices of such portable electronic notebooks, information terminals etc., those with a transparent touch panel placed on a liquid crystal display device, in particular resistance-film type touch panels, are generally adopted in view of cost, etc.
The type of resistance-film type touch panel generally used is that having a structure in which a transparent conductive film and a glass with a transparent conductive thin layer are disposed with an appropriate gap therebetween. When the transparent conductive film disposed on the exterior is pressed with a finger or a pen and brought into contact with the glass having a transparent conductive thin layer, electric current passes at that point. Conventionally, the transparent conductive film is a transparent conductive thin layer made of indium tin oxide (referred to as “ITO”, hereinafter) or the like, formed on the lower surface (surface opposed to the glass) of a substrate film, such as a plastic film.
The substrate film for such a transparent conductive film is generally a transparent hard coat film in which a transparent hard coat layer is provided on the surface of a transparent polymer film. Such a substrate film is used to improve the durability of the transparent conductive film.
In an office environment in which input devices such as portable electronic notebooks and information terminals are used, three band fluorescent lamps, with a particular wavelength having high intensity emission, are increasingly used.
The transparent hard coat films currently incorporated in touch panels, etc., undesirably exhibit an interference fringe attributable to non-uniform thickness of the transparent hard coat layer.
Such an interference fringe attributable to non-uniform thickness of the transparent hard coat layer can theoretically be avoided by completely eliminating unevenness in the transparent hard coat layer. However, it is not easy to completely eliminate the unevenness, given the accuracy of the current film formation technology.
The interference fringe attributable to non-uniform thickness of the transparent hard coat layer can also theoretically be eliminated by making the refraction index of the transparent polymer film and the refraction index of the transparent hard coat layer the same, but it is difficult to maintain the hardness of the transparent hard coat layer when its refractive index is thus selected.
Also, when a large amount of a matting agent is added to the transparent hard coat layer to make the surface uneven, the interference fringe attributable to non-uniform thickness of the transparent hard coat layer can theoretically be eliminated. However, if the surface of the transparent hard coat layer is made uneven, the resolution of images observed through the transparent hard coat film (referred to as “transmitted resolution” hereinafter) is sacrificed.